It is Bad Karma
And since there is no fear in his eyes, I can safely say that killing Mo Shu will not eliminate the danger to humanity that is the Ace of Diamond.
It is quite impossible to eradicate a parasitic entity that can duplicate itself endlessly through the use of infections and assimilations, not to mention it is more than capable of hiding inside countless living hosts, humans or otherwise. It can also lie completely dormant for many years.
Much like a virus.
Actually, it is a fucking virus. A virus that must be eradicated to the last cell.
This is the very reason to why all research data and information pertaining to the Aces are destroyed, so some idiot somewhere cannot recreate them again for whatever reason.
If someone did, much the world might get infected, causing me to press that huge reset button. It is a metaphorical button. I have pressed it once. I hope that I don't have to press again.